A cylindrical rotor is eccentrically arranged in said working chamber, said rotor having two blades which are arranged in recesses in the rotor and which during operation are pressed against the inner surfaces of the working chamber, for thereby inducing a first pumping effect so as to transport the material in first partial volumes with a first pulsating characteristic having two maxima and two minima for every full rotation of the rotor.
Such pumps are generally used in the food industry for the transportation of raw material. The raw materials often consist of an inhomogeneous material which, may contain bits or pieces which during the transportation, are subjected to undesired comminution.
This is especially the case when the raw materials are transported in closed systems, something which is desirable when transporting easily tainted raw materials which have to be protected against air or give off inconvenient odours.
The purpose underlying the present invention is the task to devise a displacement pump to be used for the transportation of inhomogeneous material in a closed transportation system, said pump having to give an effective, even and careful transportation of the material. Especially in the fish flour and the fish oil industry, wherein the raw material consists of whole fish it is desirable that the fish during the transportation from the cargo compartment in the fishing vessel to the storage tanks in a least possible degree is to be subjected to severance or other breakage. In the following the invention will be disclosed with special reference to the transportation of substantially whole fish. In order to accomplish the transportation so effectively and gently as possible through the pump this must satisfy a series of requirements. Firstly, to avoid that the fish, which is to be transported, is cut or damaged by the blades it is desirable to design the pump with as few blades as practically possible. However, when the pump has only few blades, e.g. two, the supply characteristic of the pump will be very uneven, and the inlet and the outlet of the pump must be made relatively narrow. An uneven supply characteristic is undesired as this, besides from yielding an uneven supply, unnecessarily stresses both the drive machinery and the goods of transportation.
The prior art discloses a rotating pump wherein the rotor sections which lie between the recesses of the blades are shaped so that the outer surfaces lie inside the smallest circumscribed circle of the rotor. The outer surface of the rotor is, however, formed with very abrupt profile transitions, a construction which in no way can be combined with a pivotable flap arranged between the inlet and the outlet of the pump. Further, the pump according to the prior art is equipped with four blades which is very unfavourable for pumps which are to be used for an effective, even and gentle transportation of inhomogeneous material in a closed transporting system. Besides, the pump according to this earlier German patent specification will have a very poor efficiency as the increase of volume of the working chamber obtained by the removals of the rotor cannot be utilized for an increase of the capacity of the pump because the larger part of the displacement volume which is defined between the two blades at the outlet port will be maintained between the blades and rotate together with these passed the outlet port. The removals will substantially be filled with "dead water" which spoils any increment of the pumping capacity.
From U.S. Pat. No. 1,427,053 there is known a rotating internal combustion engine wherein the rotor sections which are located between the recesses of the blades, are shaped so that the profile of the cross-section lies within the circumscribed circle of the rotor. Between the inlet and the outlet of the engine there are arranged abutment blades which are pressed against the surface of the rotor by means of springs. However, the engine according to U.S. Pat. No. 1,427,053 embodies a rotor which is concentrically arranged in the motor casing. If the engine according to U.S. Pat. No. 1,427,053 should be applied as a pump with two approximately symmetrically shaped pumping chambers, such an arrangement would firstly give rise to very narrow inlet and outlet conditions, and the shape of the pump would moreover be very unfavourable. Further, the delivery characteristic of such a modified engine used as a pump would be very uneven as the delivery would be accomplished in a shocking or impacting manner, because the two displacement principles which are based upon a rotor with displacement blades in a casing without abutment blades and a rotor without blades in a casing with abutment blades come into effect in phase and are directly summed up. For an internal combustion engine such an addition of the two displacement effects in phase is generally without signification, but in a displacement pump which is to be used for the transportation of delicate material in the food industry, and which has to perform an even delivery characteristic, this displacement principle is unacceptable. Besides, a pump designed according to the teaching of U.S. Pat. No. 1,427,053 would qualify for a pump which in neutral position allows for a short circuit or reverse flow of the transported material.